SuPHP, prevent overriding PHP ini but still allow them to set options?

On a server running with SuPHP we want to stop people from setting their own crazy values for memory/upload limits. This is easily done through /opt/suphp/etc/suphp.conf

However certain users need to be able to use things like register_globals. This needs to be specified in php.ini in their directory, but after doing the above what they add in their own php.ini has no effect.

What is the workaround for this?

Basically I dont want them to be able to modify some of the main parts of the PHP configuration e.g. memory_limit but they need to be able to add in some parts which used to be used in .htaccess